Refrigerator having variable speed compressor and control method thereof

ABSTRACT

A refrigerator and a method for controlling the same are disclosed. The refrigerator may minimize the size and material cost of the control system by controlling the internal temperature and the speed of a compressor using a thermostat used in the conventional low-capacity/low-cost refrigerator without using a system controller equipped with various sensors (internal sensors and/or external sensors) capable of controlling the internal temperature. In addition, since an inverter controller capable of controlling a BLDC compressor estimates the internal/external temperature based on operation information of the compressor, and determines the internal load, it may save energy and reduce vibrations and noise, which are the largest disadvantages of a constant-speed compressor, thereby improving satisfaction of the consumer. In addition, the BLDC compressor may be started and operated stably by applying a differentiated algorithm of the inverter controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage of International ApplicationNo. PCT/KR2018/009791, filed Aug. 24, 2018, which claims priority toKorean Patent Application No. 10-2017-0108545, filed Aug. 28, 2017, thedisclosures of which are herein incorporated by reference in theirentirety.

BACKGROUND 1. Field

The present disclosure relates to a refrigerator and a method ofcontrolling the refrigerator.

SUMMARY

It is an aspect of the present disclosure to provide a refrigerator andmethod for controlling the same, capable of controlling an internaltemperature and speed of a compressor by using operation information ofthe compressor without a sensor capable of controlling the internaltemperature.

A refrigerator and a method for controlling the same according toembodiments of the present disclosure may minimize the size and materialcost of a control system by controlling the internal temperature and thespeed of a compressor using a thermostat used in the conventionallow-capacity/low-cost refrigerator without using a system controllerequipped with various sensors (internal sensors and/or external sensors)capable of controlling the internal temperature. Furthermore, since theinverter controller capable of controlling the BLDC compressor estimatesthe internal/external temperature using operation information of thecompressor and determines an internal load, it may save energy andreduce vibrations and noise, which are the largest disadvantages of aconstant-speed compressor, thereby improving satisfaction of theconsumer. In addition, the BLDC compressor may be started and operatedstably by applying a differentiated algorithm for the invertercontroller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a structure of arefrigerator according to an embodiment.

FIG. 2 is a block diagram illustrating a refrigerator according to anembodiment.

FIG. 3 is a flowchart illustrating an inverter control algorithm of arefrigerator according to an embodiment.

FIG. 4 is a graph under a first control condition for changingcompressor speed in a refrigerator according to an embodiment.

FIG. 5 is a graph under a second control condition for changingcompressor speed in a refrigerator according to an embodiment.

FIG. 6 is a block diagram illustrating a speed controller for acompressor according to an embodiment.

FIG. 7 is a view illustrating a speed control execution cycle of acompressor according to an embodiment.

FIG. 8 is a block diagram illustrating a lead angle controller of acompressor according to an embodiment.

FIG. 9 is a view explaining a method of checking a freewheeling sectionof a compressor according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentdisclosure, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

In addition, the same reference numerals or signs given in each drawingof the present disclosure represent parts or components that performsubstantially the same function.

The terms used in the present application are merely used to describespecific embodiments and are not intended to limit the presentdisclosure. A singular expression may include a plural expression unlessotherwise stated in the context. In the present application, the terms“including” or “having” are used to indicate that features, numbers,steps, operations, components, parts or combinations thereof describedin the present specification are present and presence or addition of oneor more other features, numbers, steps, operations, components, parts orcombinations is not excluded.

In description of the present disclosure, the terms “first” and “second”may be used to describe various components, but the components are notlimited by the terms. The terms may be used to distinguish one componentfrom another component. For example, a first component may be called asecond component and a second component may be called a first componentwithout departing from the scope of the present disclosure. The term“and/or” may include a combination of a plurality of items or any one ofa plurality of items.

The embodiments of the present disclosure will now be described withreference to the accompanying drawings.

The idea of the present disclosure is basically applied tolow-capacity/low-cost refrigerators. The refrigerators may be broadlyclassified into a side-by-side type refrigerator, a bottom freezer typerefrigerator, and a top mount type refrigerator. In the side-by-sidetype refrigerator, the freezing chamber and the refrigerating chamberare arranged side by side. In the bottom freezer type refrigerator, thefreezing chamber is arranged under the refrigerating chamber. In the topmount type refrigerator, the freezing chamber is arranged above therefrigerating chamber. Although the refrigerator according toembodiments is exemplarily implemented as the side-by-side typerefrigerator for convenience of description and better understanding ofthe present disclosure, the scope or spirit of the present disclosure isnot limited thereto, and the embodiments may also be applied to thebottom freezer type refrigerator, the top mount type refrigerator, and acombination thereof.

In addition, the idea of the present disclosure may be applied to therefrigerator of the type provided in the freezer compartment as well asthe refrigerator provided in the refrigerator compartment.

FIG. 1 is a perspective view schematically illustrating a structure of arefrigerator according to an embodiment.

Referring to FIG. 1, a refrigerator 1 according to an embodiment mayinclude a box-shaped housing 10 forming an external appearance thereof,a storage chamber 20 formed in the housing 10 while being divided intoupper and lower storage chambers, a door 30 configured to open or closethe storage chamber 20, and a cooling device 40 configured to providethe storage chamber 20 with cool air.

The cooling device 40 may include a compressor 41 to compress gaseousrefrigerant, a condenser 42 to convert the compressed gaseousrefrigerant into liquid refrigerant, an expander 43 to decompress theliquid refrigerant, and an evaporator 44 to convert the decompressedliquid refrigerant into gaseous refrigerant.

The compressor 41 may be provided at a lower end of the rear surface 10d of the refrigerator 1. The compressor 41 may compress suctionedlow-temperature and low-pressure refrigerant to form high-temperatureand high-pressure refrigerant, and then discharge the high-temperatureand high-pressure refrigerant.

For this purpose, the compressor 41 may mandatorily suction therefrigerant, and compress the suctioned refrigerant to producehigh-temperature and high-pressure gas. Suctioning of the refrigerantmay be carried out using rotational force of an embedded motor 411.According to the embodiment, the compressor 41 may be a brushless directcurrent (BLDC) compressor using an inverter controller. The motor 411 ofthe BLDC compressor 41 may be rotatable at various rotational speeds,thereby controlling the flow rate of the refrigerant. The rotationalspeed of the motor 411 of the compressor 41 may be expressed in the unitof revolution per minute (RPM). Therefore, an amount or speed of therefrigerant circulation may be determined according to a degree to whichthe compressor 41 operates, for example, the rotational speed of themotor 411, and the cooling efficiency of the refrigerator 1 may also bedetermined.

In addition, the compressor 41 may include an inlet through which therefrigerant is introduced, a flow space in which the introducedrefrigerant flows, a motor rotating in the flow space and partsassociated with the motor, and an outlet through which compressedrefrigerant is discharged.

The refrigerant transferred to the compressor 41 may includeChloroFluoroCarbon (CFC), HydroChloroFluoroCarbon (HCFC),HydroFluoroCarbon (HFC), or the like. However, the refrigerant is notlimited thereto, and various kinds of materials that may be selected bya designer may be used as the refrigerant.

The compressor 41 applied in the present disclosure may include aninverter compressor, a positive displacement compressor, a dynamiccompressor, or the like.

The high-temperature and high-pressure gaseous refrigerant compressed bythe compressor 41 may be transferred to the condenser 42.

The condenser 42 may be provided on the rear surface 10 d of therefrigerator 1. If necessary, the condenser 40 may be provided at thelower end of the rear surface 10 d of the refrigerator 1 and may beexposed to the outside from the middle of the rear surface 10 d of therefrigerator 1 to facilitate heat radiation.

The condenser 42 may be connected to a discharge tube on a high-pressureside of the compressor 41 for allowing the high-temperature andhigh-pressure gaseous refrigerant compressed by the compressor 41 toexchange heat with ambient air, thereby condensing the high-temperatureand high-pressure gaseous refrigerant into liquid refrigerant. In thecondenser 42, the refrigerant emits heat to the outside while beingliquefied, and accordingly, the temperature of the refrigerant islowered.

According to the embodiment, the condenser 42 may be implemented using apipe formed to be bent into a zigzag shape. In this case, one end of thepipe may extend from a refrigerant pipe 45 connected to the compressor41, and the other end of the pipe may extend from the refrigerant pipe45 connected to the expander 43.

The expander 43 may be installed inside or outside the housing 10 of therefrigerator 1 for expanding and decompressing the high temperature andhigh pressure liquid refrigerant condensed by the condenser 42 to atwo-phase refrigerant, which is a mixture of liquid and gaseouscomponents at low temperature and low pressure, using a capillary tube.The capillary tube may be embodied by a thin tube, and the refrigerantthat has passed through the capillary tube may be decompressed anddelivered to the evaporator 44.

According to the embodiment, the capillary tube may be replaced by anexpansion valve. The expansion valve may include various types of valvessuch as a thermoelectronic expansion valve using bimetallic deformation,a thermal expansion type electronic expansion valve using volumeexpansion by heating of a sealing wax, a pulse width modulation typeelectronic expansion valve for opening or closing a solenoid valve by apulse signal, or an electronic expansion valve of a stem motor type foropening or closing the valve using a motor.

The evaporator 44 may be provided inside of the rear surface 10 d of therefrigerator 1. In this case, the evaporator 44 may be installed in thevicinity of the storage chamber 20.

The evaporator 44 may provide cold air by evaporating a low-temperatureand low-pressure liquid refrigerant expanded by the expander 43 into agaseous state.

As described above, the cooling device 40 may supply the cold air usinga phenomenon of the decompressed liquid refrigerant absorbing heatenergy from the ambient air while being converted to a gaseousrefrigerant.

The compressor 41, the condenser 42, the expander 43 and the evaporator44 are interconnected through the refrigerant pipe 45 to implement arefrigerant cycle.

The refrigerant pipe 45 may be provided to connect two of the compressor41, the condenser 42, the expander 43 and the evaporator 44, anddisposed at any position within the housing 10 of the refrigerator 1according to the designer's selection.

Meanwhile, the structure of the cooling device 40 is not limited to thecompressor 41, the condenser 42, the expander 43, and the evaporator 44.

For example, the cooling device 40 may include a peltier element thatuses a Peltier effect. The Peltier effect refers to a phenomenon when acurrent flow on a contact face between two different kinds of metals,one of the metals is subject to radiation of heat and the other issubject to absorption of heat. The cooling device 40 may supply cold airto the storage chamber 20 using the peltier element.

In another example, the cooling device 40 may include a magnetic coolingdevice that uses a magnetocaloric effect. The magnetocaloric effect mayrefer to an effect where a particular material (e.g., magnetocaloricmaterial) emits heat when magnetized and absorb heat when demagnetized.The cooling device 40 may supply cold air to the storage chamber 20using the magnetic cooling device.

In addition, a substrate assembly 46 having a processor for controllingthe refrigerator 1 may be provided inside the refrigerator 1. Thesubstrate assembly 46 may include at least one semiconductor chip andassociated components, and a substrate upon which these components maybe mounted. The semiconductor chip and associated components provided inthe substrate assembly 46 may include a processor functioning as aninverter controller 100, which will be described later, a semiconductorchip or a magnetic disk functioning as a storage. The substrate assembly46 may be electrically connected to various semiconductor chips andassociated components, a power supply 50 for supplying power to thecompressor 41 or the like.

FIG. 2 is a block diagram illustrating a refrigerator according to anembodiment.

Referring to FIG. 2, the refrigerator 1 according to an embodiment ofthe present disclosure may further include the power supply 50, athermostat 60, a filter 70, and the inverter controller 100 in additionto the cooling device 40.

The power supply 50 may supply power to various components in therefrigerator 1. The power supply 50 may be configured to receive anexternal commercial power and convert the received commercial powersupply into an appropriate voltage and/or current to be supplied to eachcomponent. Also, the power supply 50 may be implemented using a batterycapable of storing electric energy, in which case the battery may berechargeable. According to the embodiment, the power supply 50 maysupply the electric energy of a predetermined voltage and/or current tothe compressor 41 through a circuit or a separate lead provided on thesubstrate assembly 46. In this case, the power supply 50 may supply theelectric energy of the predetermined voltage and/or current to thecompressor 41 through the inverter controller 100.

The thermostat 60 may open or close a switch according to an operationof a bimetal implemented by two alloy plates having different expansioncoefficients. The thermostat 60 may electrically link the power supply50 and the inverter controller 100 according to the internal temperatureof the inside of the storage chamber 20.

Particularly, the thermostat 60 may allow power to be applied to theinverter controller 100 by electrically connecting the power supply 50and the inverter controller 100 as the bimetal bends and puts thecircuit in a conducting state when the internal temperature of thestorage chamber 20 increases.

As described above, the thermostat 60 may be in the conducting state asthe internal temperature of the storage chamber 20 increases, and thepower supplied from the power supply 50, that is, an electrical signal,may be applied to the inverter controller 100 through the thermostat 60.

Therefore, when the circuit is put in the conducting state by thethermostat 60, the inverter controller 100 may drive the motor 411 ofthe compressor 41 to be rotated.

The filter 70 may be connected between the power supply 50 and theinverter controller 100, and may block switching noise generated whenthe compressor 41 is controlled.

The inverter controller 100 may include a converter 110, a smoothingcapacitor 120, an inverter 130, a current sensor 150, a voltage sensor160, and a controller 170.

The converter 110 may be connected between the power supply 50 and theinverter 130, and may rectify alternating current (AC) power suppliedfrom the power supply 50 to output DC link voltage.

For example, the converter 110 may be comprised of a half-waverectification circuit of diodes, and may convert the AC power suppliedfrom the power supply 50 to DC power by half-wave rectification.

In addition, the converter 110 may perform full-wave rectification ofthe AC power source by connecting four switching elements Q1 to Q4 inthe form of a high bridge as illustrated in FIG. 2 instead of theconventional diodes.

The smoothing capacitor 120 may be connected between the converter 110and the inverter 130 to smooth and convert a voltage output from theconverter 20 into DC.

The inverter 130 may change a DC voltage output from the smoothingcapacitor 120 into a pulsed three-phase AC (U, V, W) having an arbitraryvariable frequency through pulse width modulation and drive the motor411 of the compressor 41. The inverter 130 is an ordinary switchingcircuit for inverting a DC voltage into three-phase AC by connecting sixswitching elements Q5 to Q10 and a freewheeling diode into a three-phasefull bridge and applying the three-phase AC to the motor 411.

The six switching elements Q5 to Q10 may include high voltage switchingdevices such as high voltage bipolar junction transistors, high voltagefield effect transistors, or insulated gate bipolar transistors (IGBTs).

For example, the inverter 130 may be a voltage source inverter of athree-phase full bridge type. Particularly, in the inverter 130, sixswitching elements Q5 to Q10 are interconnected. More particularly,three upper switching elements Q5, Q7 and Q9 may be connected inparallel with one another, and three lower switching elements Q6, Q8 andQ10 may be connected in parallel with one another. The three upperswitching elements Q5, Q7 and Q9 and the three lower switching elementsQ6, Q8 and Q10 may be connected in series one to one. The three upperswitching elements Q5, Q5, Q7 and Q9 and the lower switching elementsQ6, Q8 and Q10 may be connected to the motor 411.

The current sensor 150 may detect a current flowing in the winding ofthe internal motor 411 of the compressor 41 by using a shunt resistor151 connected to the lower ends of the switching elements Q3 and Q4 ofthe converter 110. The current sensor 150 may detect the current flowingin the shunt resistor 151 with an input of a voltage across the shuntresistor 151, and may send the detection result to the controller 170.

The voltage sensor 160 may be connected to a DC link stage and maydetect the voltage applied to the winding of the internal motor 411 ofthe compressor 41 using the DC link voltage across the DC link stage.The voltage sensor 160 may detect the DC link voltage produced by thecurrent entering the DC link stage from the power supply 50 and send thedetection result to the controller 170.

The controller 170 may control the converter 110 and the inverter 130 byoutputting a pattern of a PWM signal supplied to the converter 110 andthe inverter 130. The controller 170 may be implemented by amicroprocessor (MCU) that controls the switching elements Q1 to Q10 ofthe converter 110 and the inverter 130 to be turned on or off.

The controller 170 may also include a timer that counts operation timeof the compressor 41.

The controller 170 may calculate the current power consumption of thecompressor 41 by using the voltage applied to the winding of the motor411 and the current flowing in the winding of the motor 411, and maychange operation speed of the compressor 41 by estimating the internaltemperature of the storage chamber 20 based on the calculated currentpower consumption of the compressor 41.

The controller 170 may also change the operation speed of the compressor41 by estimating the external temperature using the current operationspeed and the operation time of the compressor 41.

Operations and effects of a refrigerator and method for controlling thesame according to an embodiment of the present disclosure will now bedescribed in detail.

FIG. 3 is a flowchart illustrating an inverter control algorithm of therefrigerator according to an embodiment.

Referring to FIG. 3, when an initial internal temperature increases, thethermostat 60 operates (200), allowing the inverter controller 100 to bepowered (202).

At this time, the inverter controller 100 is powered for the first time,so it has no information about the refrigerator 1, e.g., informationabout a state of the refrigerant cycle.

Accordingly, the controller 170 may count time after the initial poweris applied to the inverter controller 100, and determine whether thecounted time elapses by a set delay time Td (i.e., a time (about 2minutes, 1 minute, or 30 seconds) for protecting the compressor fromstart failure) (204).

When the initial power is applied to the inverter controller 100 and thecounted time elapses by the delay time Td (204), the controller 170switches the inverter 130 to turn on the compressor 41 (206).

When the compressor 41 is started, an oil pumping operation is performedto smoothly operate the mechanical part of the compressor 41 (208). Aspring type oil pumping structure is employed in the motor 411 of theBLDC compressor 41 to supply oil to the compressor 41 when thecompressor 41 is operated.

After the oil pumping operation, the compressor 41 may be operated atlow speed for a predetermined time (about 10 minutes) (210).

During the low speed operation of the compressor 41, the controller 170calculates the current power consumption Wc of the compressor 41 usingthe voltage applied to the winding of the motor 411 and the currentflowing in the winding of the motor 411 (212).

The controller 170 compares the calculated current power consumption Wcof the compressor 41 with reference power Ws (214), and estimates theinternal temperature of the storage chamber 20 and control the operationspeed of the compressor 41.

When the power consumption Wc is equal to or higher than the referencepower Ws (214), the controller 170 determines that the storage chamber20 is in a high load state where the internal temperature is high andoperate the compressor 41 at high speed (216). The controller 170 goesback to operation (212) and performs subsequent operations starting fromoperation (212).

In this way, when the current power consumption Wc of the compressor 41is equal to or higher than the reference power Ws, the controller 170may determine that the internal temperature condition is high ascompared to the cooling ability, and increase the operation speed of thecompressor 41 to execute high cooling ability.

When the power consumption Wc is less than the reference power Ws (214),the controller 170 may determine that the internal temperature of thestorage chamber 20 is in an appropriate load state.

Next, the controller 170 compares the operation time Tc of thecompressor 41 with reference time Ts (218), and estimates the externaltemperature and control the operation speed of the compressor 41.

When the operation time Tc of the compressor 41 is equal to or more thanthe reference time Ts (218), the controller 170 determines that theexternal temperature is high and proceed to operation 216 to operate thecompressor 41 at the high speed.

In this way, when the current power consumption Wc of the compressor 41is less than or the reference power Ws and the operation time Tc of thecompressor 41 is equal to or more than the reference time Ts, thecontroller 170 may determine that the internal temperature condition isappropriate for the cooling ability but the external temperaturecondition is high as compared to the cooling ability, and increase theoperation speed of the compressor 41 to execute high cooling ability.

When the operation time Tc of the compressor 41 is less than thereference time Ts (218), the controller 170 may determine that theexternal temperature is in the appropriate state and proceed tooperation 210 to operate the compressor 41 at the low speed.

In this way, when the current power consumption Wc of the compressor 41is less than the reference power Ws and the operation time Tc of thecompressor 41 is less than the reference time Ts, the controller 170 maydetermine that the refrigerator 1 is in a proper load state for thecooling ability meets both the internal temperature and the externaltemperature. The controller 170 may thus operate the compressor 41 atlow speed, thereby increase energy efficiency and reducing noise andvibrations.

Next, a method of changing the operation speed of the compressor 41 byestimating the internal temperature of the storage chamber 20 based onthe current power consumption Wc of the compressor 41 will be describedin more detail with reference to FIG. 4.

FIG. 4 is a graph under a first control condition for changingcompressor speed in a refrigerator according to an embodiment.

Referring to FIG. 4, the controller 170 may estimate the internaltemperature by calculating the current power consumption of thecompressor 41 based on information generated while the compressor 41 isoperating at the low speed, e.g., the voltage applied to the winding ofthe motor 411 in the compressor 41 and the current flowing in thewinding of the motor 411, and may control the operation speed of thecompressor 41.

More particularly, the controller 170 may estimate the internaltemperature of the storage chamber 20 by comparing the power consumptionWc with the reference power Ws.

First, when the power consumption Wc is higher than the reference powerWs, the controller 170 may determine that the storage chamber 20 is in ahigh load state where the internal temperature is high, and require ahigh cooling ability to prevent the food stored in the refrigerator 1from going bad. To execute the high cooling ability, the controller 170may increase the operation speed of the compressor 41 to control theinternal temperature to be lowered, thereby maintaining normal cool airin the storage chamber 20 (refer to the high load operation of FIG. 4).

Since the load of the refrigerator 1 varies depending on the number ofopening and closing times of a door 30, the external temperature, thefood storage amount, and the temperature of the food, the controller 170may be able to change the operation speed of the compressor 41 tomaintain the normal cool air.

When the power consumption Wc is less than the reference power Ws, thecontroller 170 may determine that the storage chamber 20 is in a lowload state where the internal temperature is low, and require loweringof the cooling ability. To lower the cooling ability, the controller 170may reduce the operation speed of the compressor 41 to control theinternal temperature to be maintained to maintain normal cool air in thestorage chamber 20 (refer to the low load operation of FIG. 4).

Referring to FIG. 4, initial operation is represented by operation speedof the compressor 41 when the refrigerator 1 is started first. When thepower consumption Wc is equal to or higher than the reference power Ws10 minutes after the low speed operation, the compressor 41 may bedriven to be switched into the high speed operation mode (refer to{circle around (a)} of FIG. 4).

The controller 170 may change the operation speed of the compressor 41according to the internal temperature by setting the reference power Wsfor each step of the operation speed of the compressor 41. For example,the reference power Ws may be set to several steps Ws1, Ws2, Ws3, . . ., and the operation speed of the compressor 41 may be controlled to varyaccording to comparison between the power consumption Wc and thereference power Ws1, Ws2, Ws3, or the like.

In addition, a method of changing the operation speed of the compressor41 by estimating the external temperature based on continuous operationtime of the compressor 41 will be described in more detail withreference to FIG. 5.

FIG. 5 is a graph under a second control condition for changing thecompressor speed in a refrigerator according to an embodiment.

Referring to FIG. 5, the controller 170 may control the operation speedof the compressor 41 by estimating an external temperature byaccumulating information generated while the compressor 41 is operatingat low speed, e.g., time during which the compressor 41 is operating.

Next, a start and operation algorithm of the BLDC compressor 41 used inthe low-capacity/low-cost refrigerator 1 of the present disclosure willbe described.

The thickness, size, and weight of the rotor or stator of the motor 411may be minimized in order to reduce the cost of the internal motor 411of the BLDC compressor 41 applied to the refrigerator 1 of the presentdisclosure. In this case, centrifugal force and inertia of the motor 411are reduced, making it difficult to detect the position at the initialstart and leading to start failure. In addition, when instantaneouspower failure occurs during the operation of the compressor 41, theremay be a differential pressure according to the refrigerant cycle of therefrigerator 1. At this time, when the BLDC compressor 41 is started, itmay end up in start failure and making noise.

Accordingly, the inverter controller 100 may have the following startalgorithm to increase the magnitude of the start current relative to thesame voltage by applying a voltage to a region where a backelectromotive force is small at the initial start of the compressor 41.

The voltage equation of the motor 411 may be expressed in the followingequation (1):V=IR+L×di/dt+e  (1).

where, V is the voltage of the motor 411, I is the current flowing inthe motor 411, R is a winding resistance of the motor 411, Lisa windinginductance of the motor 411, di/dt is a current slope per hour, and e isthe back electromotive force generated as the motor 411 rotates.

L×di/dt is ignorable at the initial start of the compressor 41.Therefore, I may be expressed by (V−e)/R, in which case since V and Rare constant, when the voltage is applied in the region where e issmall, a relatively large current may flow, so that the disadvantage ofthe initial start may be compensated.

Also, as the motor 411 shrinks, the BLDC compressor 41 may generateripples in the low speed operation region.

To prevent the ripples, a speed control execution cycle may be set to aswitching frequency cycle that is used for controlling the BLDCcompressor 41. In this case a speed error may be obtained in a shorttime to change and apply the voltage, enabling relatively high accuracyin speed control and accordingly suppressing generation of the ripples.This will be described with reference to FIGS. 6 and 7.

FIG. 6 is a block diagram illustrating a speed controller of acompressor according to an embodiment, and FIG. 7 is a view illustratinga speed control execution cycle of the compressor according to anembodiment.

Referring to FIG. 6, the speed controller 180 may use a PI controller181 to control voltage output (duty) value V* according to the controltarget speed based on an input value for an error between a commandspeed ω* and a current speed ω. The voltage output value V* may befinally output through a filter 182 as a value within a limited range.

The inverter 130 may operate the switching elements Q5 to Q10 and IGBTbased on the output voltage to drive the motor 411, and detect a zerocrossing point (ZCP) with a ZCP detector 183 through neutral pointvoltages Ea, Eb, and Ec of the respective phases to estimate the currentspeed ω.

Accordingly, the inverter controller 100 may calculate a powerconsumption value, and determine operation speed based on the calculatedpower value. The operation speed may be the command speed ω*.

The neutral point voltages Ea, Eb, and Ec of the respective phases (Uphase, V phase, W phase) may be detected during the operation of themotor 411, in which case a point where the neutral point voltage becomesVdc/2 may be determined as a ZCP, and the current speed ω may beestimated based on the time taken for detection between the ZCP and thenext ZCPZCP.

The PI controller 181 may be a controller that calculates an errorbetween an output value and a reference value and calculates a controlvalue necessary for control based on the error value, and have astructure in which a proportional (P) controller and an integration (I)controller operate in parallel. The PI controller 181 of the speedcontroller 180 may receive the error between the target speed and thecurrent speed and output an operation voltage for the IGBT.

As illustrated in FIG. 7, when an execution cycle of the speedcontroller 180 is synchronized with a switching frequency cycle (e.g.,1125 μsec of a carrier frequency 8 KHz), the voltage may be changed forthe speed error and applied in short time, thereby enabling relativelyaccurate speed control.

In addition, the inverter controller 100 may perform the followingcontrol to perform the speed control.

When a PWM duty is less than 100%, the speed may be controlled by fixinga lead angle but changing the PWM duty.

Then, when the load increases or the high speed region is reached, thecontroller 170 may fix the PWM duty to 100% and control the lead angleby 14° to 30° to change the speed. This will be described with referenceto FIG. 8.

FIG. 8 is a block diagram illustrating a lead angle controller of acompressor according to an embodiment.

Referring to FIG. 8, the lead angle controller 190 may operate after theduty becomes 100%, and control the voltage output (duty) value throughthe speed controller 180 when the duty is less than 100%. When the leadangle controller 190 is operating, the duty is fixed at 100%, and thelead angle controller 190 may use the PI controller 191 to output a leadangle value Ø* according to a control target speed based on the inputvalue for the speed error between the command speed ω* and the currentspeed ω. The output lead angle value may be controlled to be a value of14° to 30° through the filter 192.

The inverter 130 may operate the switching elements Q5 to Q10 and IGBTbased on the output voltage to operate the motor 411, and detect ZCPswith the ZCP detector 183 through neutral point voltages Ea, Eb, and Ecof the respective phases to estimate the current speed ω.

Accordingly, the inverter controller 100 may calculate a powerconsumption value, and determine operation speed based on the calculatedpower value. The operation speed may be the command speed ω*.

The neutral point voltages Ea, Eb, and Ec of the respective phases (Uphase, V phase, W phase) may be detected during the operation of themotor 411 and a point where the neutral point voltage becomes Vdc/2 maybe determined as a ZCP, and the current speed ω may be estimated basedon time taken for detection between the ZCP and the next ZCP.

The PI controller 191 may be a controller that calculates an errorbetween an output value and a reference value, and calculates a controlvalue necessary for control based on the error value, and have astructure in which a proportional (P) controller and an integration (I)controller operate in parallel. The PI controller 191 of the lead anglecontroller 190 may receive an error between target speed and the currentspeed to output the lead angle value.

In addition, the inverter controller 100 may require a large amount ofcurrent when operating the BLDC compressor 411 in an overload region. Afreewheeling current may be generated by an intelligent power module(IPM) switching of the inverter controller 100 when the current in thewinding of the motor 411 increases. The freewheeling current may causewrong ZCP detection and abnormal operation and stopping of the BLDCcompressor 411.

In order to prevent the wrong ZCP detection, the inverter controller 100of the present disclosure may check a freewheeling section before theZCP detection.

In this way, by checking the freewheeling section before the ZCPdetection, the BLDC compressor 41 may operate normally even in theoverload region. A method of checking the freewheeling section will bedescribed with reference to FIG. 9.

FIG. 9 is a view explaining a method of checking a freewheeling sectionof a compressor according to an embodiment.

Referring to FIG. 9, when the ZCP detection is set from Low to High, theinverter controller 100 may be set to less than ⅞ of the DC linkvoltage. When the ZCP detection is set from High to Low, the invertercontroller 100 may be set to more than ⅛ of the DC link voltage.

As described above, it is possible to compensate for start failure andnoise of the compressor 41 through the specialized algorithm of theinverter controller 100.

While the present disclosure has been particularly described withreference to exemplary embodiments, it should be understood by those ofskilled in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present disclosure.

The invention claimed is:
 1. A refrigerator comprising: a housingforming an external appearance of the refrigerator, and including astorage chamber; a thermostat configured to operate according to aninternal temperature of the storage chamber; a compressor comprising amotor and configured to be operated according to operation of thethermostat; an inverter controller comprising a plurality of switchingelements and configured to control an operation speed of the compressorby operating the switching elements to operate the motor, based onoperation information of the compressor; and a speed controllerconfigured to transmit an output voltage to the inverter controller andcontrol a duty ratio of the output voltage, wherein the invertercontroller is configured to calculate power consumption of thecompressor using a voltage applied to a winding of the motor in thecompressor and a current flowing in the winding of the motor, andcontrol the operation speed of the compressor based on the calculatedpower consumption of the compressor, wherein the inverter controller isconfigured to operate the switching elements based on the duty ratio, sothat the switching elements operate at a switching frequency periodcorresponding to the duty ratio, and wherein the speed controller isconfigured to execute a speed control at an execution period, which isthe same as the switching frequency period, so that the speed controland operation of the switching elements are synchronized.
 2. Therefrigerator according to claim 1, wherein the inverter controller isconfigured to change the operation speed of the compressor by estimatingthe internal temperature based on the calculated power consumption. 3.The refrigerator according to claim 2, wherein the inverter controlleris configured to compare the power consumption with a reference power,determine that the internal temperature is high when the powerconsumption is equal to or higher than the reference power and increasethe operation speed of the compressor.
 4. The refrigerator according toclaim 3, wherein the inverter controller is configured to set thereference power for different operation speeds of the compressor andchange the operation speed of the compressor stepwise according to theinternal temperature.
 5. The refrigerator according to claim 2, whereinthe inverter controller is configured to compare the power consumptionwith a reference power, determine to be in a load condition where theinternal temperature is appropriate when the power consumption is lessthan or equal to the reference power, and operate the compressor at aspecified speed that is less than a maximum speed.
 6. The refrigeratoraccording to claim 1, wherein the inverter controller is configured tochange the operation speed of the compressor by estimating an externaltemperature based on the operation speed or an operation time of thecompressor.
 7. The refrigerator according to claim 6, wherein theinverter controller is configured to compare the operation time of thecompressor with a reference time, determine that the externaltemperature is high when the operation time is equal to or higher thanthe reference time and increase the operation speed of the compressor.8. The refrigerator according to claim 6, wherein the invertercontroller is configured to compare the operation time of the compressorwith reference time, determine to be in a load condition where theexternal temperature is appropriate when the operation time is less thanor equal to the reference time, and operate the compressor at aspecified speed that is less than a maximum speed.
 9. The refrigeratoraccording to claim 2, wherein the thermostat is configured to be in aconducting state when the internal temperature increases beyond a setpoint as the internal temperature increases and apply power to theinverter controller.
 10. The refrigerator according to claim 9, whereinthe inverter controller is configured to operate a brushless directcurrent (BLDC) motor in the compressor when a circuit is in a conductingstate by the thermostat.
 11. The refrigerator according to claim 1,further comprising: a filter configured to block switching noisegenerated in controlling the compressor.
 12. A refrigerator comprising:a brushless direct current (BLDC) compressor comprising a motor; athermostat configured to transmit an electrical signal according to aninternal temperature of a storage chamber; an inverter controllercomprising a plurality of switching elements and configured to operatethe BLDC compressor at a specified speed according to the electricalsignal transmitted from the thermostat, wherein the specified speed isless than a maximum speed; and a speed controller configured to transmitan output voltage to the inverter controller and control a duty ratio ofthe output voltage, wherein the inverter controller is configured tocalculate power consumption of the BLDC compressor using a voltageapplied to a winding of the motor in the BLDC compressor and a currentflowing in the winding of the motor during operation of the BLDCcompressor at the specified speed, and control an operation speed of theBLDC compressor by estimating the internal temperature based on thecalculated power consumption, wherein the inverter controller isconfigured to control the operation speed by operating the switchingelements to operate the motor, wherein the inverter controller isconfigured to operate the switching elements based on the duty ratio, sothat the switching elements operate at a switching frequency periodcorresponding to the duty ratio, and wherein the speed controller isconfigured to execute a speed control at an execution period, which isthe same as the switching frequency period, so that the speed controland operation of the switching elements are synchronized.
 13. Therefrigerator according to claim 12, wherein the inverter controller isconfigured to control the operation speed of the BLDC compressor byestimating an external temperature using the operation speed or anoperation time of the BLDC compressor.
 14. The refrigerator according toclaim 13, wherein the inverter controller is configured to set areference power for different operation speeds of the BLDC compressorand change the operation speed of the BLDC compressor stepwise accordingto the internal temperature.
 15. A method of controlling a refrigeratorincluding a housing having a storage chamber formed therein, athermostat configured to operate according to an internal temperature ofthe storage chamber, a compressor comprising a motor and configured tobe operated according to operation of the thermostat, and an invertercontroller comprising a plurality of switching elements, the methodcomprising: calculating power consumption of the compressor by detectinga voltage applied to a winding of the motor in the compressor and acurrent flowing in the winding of the motor; comparing the calculatedpower consumption with reference power, and increasing an operationspeed of the compressor when the power consumption is equal to or higherthan the reference power; operating the compressor at a specified speedthat is less than a maximum speed when the power consumption is lessthan the reference power; and performing speed control according to anoutput voltage, to control the switching elements to operate at aswitching frequency period corresponding to a duty ratio of the outputvoltage so as to operate the motor, thereby changing the operation speedof the compressor, wherein the speed control is executed at an executionperiod, which is the same as the switching frequency period, so that thespeed control and operation of the switching elements are synchronized.16. The method according to claim 15, further comprising: setting thereference power for different operation speeds of the compressor andincreasing the operation speed of the compressor stepwise according tothe internal temperature.
 17. The method according to claim 15, furthercomprising: counting an operation time of the compressor and comparingthe operation time with a reference time; increasing the operation speedof the compressor when the operation time is equal to or higher than thereference time; and operating the compressor at the specified speed whenthe operation time is less than the reference time.
 18. The methodaccording to claim 15, wherein the compressor comprises a brushlessdirect current (BLDC) compressor.